A thin film of indium-antimony compound has a higher mobility (78,000 cm.sup.2 /V.multidot.sec) than other semiconductor compounds, such as an indium-arsenic compound (30,000 cm.sup.2 /V.multidot.sec) and gallium-arsenic compound (7,000 cm.sup.2 /V.multidot.sec). Because of this property, a thin film of indium-antimony compound is known to be advantageous for use as a Hall element or magnetoresistive element, and has been getting the increasing attention of researchers as a device that can be used in a position detector for a direct drive motor, or as a component of video tape recorder or acoustic equipment.
Two important parameters for the Hall effect of a semiconductor are the Hall coefficient (R.sub.H) and Hall mobility (.mu..sub.H). FIG. 1 shows an arrangement for measurement of these two parameters, which consists of a test conductor A having a length l, width w, and a thickness t (not illustrated), on which gold is vacuum-deposited to form input electrodes a, a' and output electrodes b, b'. A voltage V.sub.Hi is developed between the output electrodes when the input electrodes are connected to a constant current supply I, and a voltage V.sub.Hv is developed when they are connected to a constant voltage supply V. The two voltages are represented by the following equations: ##EQU1## wherein B is the magnetic flux density of an external magnetic field applied, and f is a factor dependent on the configuration of the sample. As equation (1) shows, V.sub.Hi is in inverse proportion to the thickness of the material through which the current flows, and it can be seen that the thickness of an indium-antimony wafer to be used as a high-sensitivity Hall element or magnetoresistive element should be as small as possible. Since the indium-antimony semiconductor has a small forbidden band, its Hall coefficient (R.sub.H) in equation (1) varies greatly with temperature, and V.sub.Hi, the output voltage under constant current, is largely dependent on temperature in practical applications. On the other hand, the Hall mobility (.mu..sub.H) in equation (2) is fairly independent with respect to temperature and almost all commercial indium-antimony Hall elements are used under constant voltage. Hence, an indium-antimony semiconductor having high Hall mobility rather than high Hall coefficient is desired. However, no industrial process has to date been known for producing a thin film of indium-antimony crystalline structure.
Heretofore, it has been considered essential that in a compound semiconductor such as indium-antimony, the atomic ratio of the element of group IIIB in the Periodic Table to the element of group VB should be 1/1 (see Z. Naturforschung, Vol. 7a, p. 744, 1952). To make a wafer of indium-antimony crystal having an In to Sb atomic ratio of 1/1 for use as a Hall element of magnetoresistive element, a slice of a single crystal of indium-antimony is polished into a thin film, or an indium-antimony composition having a thickness of about 10 .mu.m layer is formed on a substrate by vacuum deposition or other suitable means, crystallized by zone melting and then polished to a thin film (see Japanese Patent Application (OPI) No. 9373/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")). However, slicing a wafer of InSb single crystal is not an industrially advantageous method, since a large amount of expensive material must be used. In the second method wherein the vacuum-deposited InSb layer is crystallized, controlling the In to Sb atomic ratio at 1/1 is very difficult and requires complex procedures, and these are two great limiting factors on the effort to use this method on an industrial scale. K. G. Gunther proposed in U.S. Pat. No. 3,172,778 a process for making a thin layer of IIIB-VB compound semiconductor by vacuum deposition. In that process, Gunther suggests presetting the temperature of the substrate higher than the decomposition temperature of the compound semiconductor, and depositing more element of VB group than the element of IIIB by controlling the arrival rate ratio of the two elements (hereunder referred to as A.sub.In /A.sub.Sb) to be 1 or less. The arrival rate ratio (A.sub.In /A.sub.Sb) as used herein means the ratio of the flux density of In atoms to that of Sb atoms that reach the substrate in the process of vacuum deposition (see Physics Status Solid, (a), Vol. 54, p. 707, 1979). But even this method requires a complex procedure to control the atomic ratio of In to Sb to be 1.0/1 and has the above described defects of the conventional art.
Noting that in the prior art the problem in producing a thin film of indium-antimony semiconductor is the necessity of strictly controlling the In to Sb atomic ratio, and that therefore the process control can be simplified and hence the desired thin film can be easily produced by expanding the latitude in selection of the In to Sb atomic ratio, the present inventors have conducted various studies to develop an industrial process for making a thin film of indium-antimony crystalline structure.